Machines for spinning or twisting yarn generally comprise at least two kinds of working units, each of which is associated with a drive mechanism having at least one prime mover or motor, preferably an electric motor, so that on interruption of the energy supply the rotational speed of each of the drive mechanisms drops alone or together with the rotational speed of the remaining ones of the drive mechanisms from an operational value of the rotational speed.
The machines with which the invention is concerned can be ring spinning frames, ring twisting frames, open-end-rotor spinning frames, open-end friction spinning frames, or the like.
The common feature of all these machines is that they produce spun or twisted thread, fiber, yarn, or the like generally referred to as yarn herein. For the purposes of this application, moreover, a twisted yarn is considered to be a variant of a spun fiber yarn.
As the starting material for the spun or twisted yarn, for example, spun fibers, endless fibers, or filaments can be used.
The working units can be, for example, spindles, rotors, yarn-releasing or disentangling rollers, drafting rollers or frames, or the like.
The torque or force transfer from the electric motor and/or drive mechanism to the working unit is effected for example by shafts, tangential belts, or the like.
Various kinds of working units, each operated by its individual drive mechanism during normal operations, have suitable inputs to the corresponding motors to provide at least approximately constant rotational speed ratio between the units.
However during an abnormal operation, when either one motor is cut off from the power supply or the power supply fails to one or more motors, the approximately constant rotational speed ratio or relationship is no longer guaranteed, since then the working unit driven by the motor cut off from the power supply comes to a standstill.
Furthermore the drive mechanisms with the various working units have different speed fall off or run down characteristics and different run down times from the normal rotational operational speeds to standstill.
As a result, during such run down faults can occur in the product, for example, due to overspinning of the yarn. In some cases these faults are accompanied by more serious events, for example yarn breaking.
In abnormal operating conditions, for example, power failure, anomalous operating conditions occur immediately which lead to machine stoppages and product damage.